1. Field of the Invention
This invention relates to a method for making a semiconductor device and especially relates to a method for making a semiconductor device having a projecting electrode (referred to hereafter as a bump electrode) connecting to another electrode.
2. Description of the Related Art
First of all, a wire bonding type semiconductor device which is used for a wire bonding system to make a final semiconductor device will be explained with reference to FIG. 1(a) and FIG. 4 showing a cross sectional view thereof and a partial enlarged cross sectional view thereof respectively.
In these figures, a semiconductor device comprises a semiconductor substrate 1, and a semiconductor element 12, for example a MOS transistor, is provided in the semiconductor substrate 1, as shown in FIG. 4.
And further, on the semiconductor substrate, at least one electrode pad 2 is provided so as to electrically connect to the external terminal of the wiring on the surface of the substrate on which the semiconductor device will be mounted, and the electrode pad 2 and each of the semiconductor element 12 are electrically connected to each other with the wiring means 13 consisting of, for example, Al or the like.
Generally, the electrode pad 2 and the wiring means 13 are usually made of the same material.
Moreover, as shown in these figures, a passivation film 3 consisting of, for example, a SiO.sub.2, SiN film, Al.sub.2 O.sub.3 film, or the like, is formed on the surface of the semiconductor device as a deactivation treatment in order to reduce the unfavorable effects caused by a contamination on the surface of the semiconductor element or an electrolysis thereof, and after that an opening is formed by selectively removing a portion of the passivation film 3 mounted on the electrode pad 2.
A type of semiconductor device such as mentioned above is usually die-bonded in a face-up condition to a surface of a substrate 14 as shown in FIG. 5 and the electrode pad 2 of the semiconductor device is connected to a terminal 15 on the surface of the substrate 14 by a wire 16 using a wire-bonding method.
However, the wire bonding type semiconductor device as described above, normally has an advantage in that it usually has a relatively high degree of freedom in wiring, although it also has such deficits such as the strength of the connecting portion thereof is rather weak due to the connecting portion being formed by such a wire bonding method and a monopolized area for such a bonding portion is naturally increased.
Further, there is another problem wherein such a wire bonding type semiconductor device has an inferior characteristic of a resistance to its environment because it is mounted on the substrate by the face-up method.
On the other hand, generally speaking, since an initial breakdown ratio of the semiconductor device usually comes to about 30% of the total number of breakdowns thereof as a breakdown mode of the semiconductor device, a reliability check is usually carried out for each semiconductor device by way of a burn-in test before the shipment thereof.
However, when such a wire bonding type semiconductor device as described above is once assembled into a substrate, to make, for example, a hybrid integrated circuit, it is impossible for the semiconductor devices to be exchanged each other, and accordingly, if a semiconductor device having a low reliability is detected, the entire hybrid integrated circuit per se should be scrapped resulting in higher production costs.
Accordingly, in recent years, a so called flip chip type semiconductor device having a wiring with bump electrodes on the surface thereof and being mounted on a surface of a substrate in such a way that the surface thereof having wiring with bump electrodes is directed downwardly in a face down condition to make an electrical connection between the bump electrode and the terminal on the surface of the substrate without using any wiring, is used frequently in this field.
A typical flip chip type semiconductor device as mentioned above is disclosed in Japanese Unexamined Patent Publication No. 59-161051.
This flip chip type semiconductor device described above for instance has an advantage that since it uses no wiring to make a connection, a monopolized area for a bonding portion is reduced to a great extent and it has a superior characteristic of resistance to its environment.
Further, in such a flip chip type semiconductor device, the production cost can be reduced because it can be easily replaced after assembly by only heat treating the bump electrode portion to melt the solder.
However, once after the flip chip type semiconductor device is designed and produced, it is difficult for the bump electrode location to be replaced and the degree of freedom of wiring thereof is small, for example, when a wiring pattern or the like on the surface of the substrate on which said semiconductor device is mounted, is changed, a new design thereof is required even if the required performance is still unchanged, and accordingly this kind of semiconductor device has disadvantages over the production of multiple kinds of devices in lower quantities because of the necessary time and cost for producing the semiconductor device including the semiconductor element. In the method for making such a flip chip type semiconductor device disclosed in Japanese Unexamined Patent Publication No.59-161051, the first step thereof is preparing the substrate including only a semiconductor element therein.
Accordingly, in this method, there are many steps required in the course of manufacturing the final object of the semiconductor device causing the process per se to be complicated and the production cost to be increased.
And further, in Japanese Unexamined Patent Publication No.59-161051, the object thereof is to provide a semiconductor device having a size as small as possible, and for that reason, the bump electrode is arranged on the center of the semiconductor device.
But in such a configuration, since the passivation film of the substrate, on the surface of which the bump electrodes are mounted, is generally so weak that it can be easily cracked and broken, SiN film is used to prevent the occurrence of such cracks or breakages.
However, the use of SiN film as a passivation film will result in some restrictions of the manufacturing process causing the degree of freedom of the material selection to be decreased and making the process more complicated and the production cost higher.
Further, in the prior art, as the semiconductor device has a special configuration, when its design is to be modified, it is required to redesign it again entirely from the starting material, reducing the development speed and increasing the development cost.